Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 041614
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
1014 AM MDT TUE AUG 4 2015

.UPDATE...

NEGATIVELY TILTED UPPER TROF SLOWLY DRIFTING NORTHEAST OVER
NORTHERN WYOMING IS CREATING A VERY FAVORABLE HEAVY RAIN PATTERN
FOR SOUTHERN MONTANA AND NORTHERN WYOMING TODAY. PRECIPITABLE
WATER VALUES OVER 1.25 INCHES AND SLOW STORM MOVEMENT COMBINED
WITH PERSISTENT DIVERGENCE ALOFT WILL BRING THE POTENTIAL FOR
LOCALLY HEAVY RAIN WITH ANY STORMS TODAY...ESPECIALLY FROM
BILLINGS EAST WHERE FLASH FLOODING CONCERNS ARE INCREASING.
ALREADY HAVE A FLASH FLOOD WARNING OUT FOR BIG HORN COUNTY WITH
A PERSISTENT LINE OF STRONG THUNDERSTORMS THERE. AS A MID LEVEL
IMPULSE WORKS IN FROM THE WEST THIS AFTERNOON WILL SEE A LINE OF
SHOWERS AND STORMS WORK ACROSS THE AREA FROM WEST TO EAST INTO THE
LATE EVENING. WIDESPREAD PRECIPITATION VALUES OF .2 TO .5 INCHES
CAN BE EXPECTED TODAY...WITH LOCALLY 1 TO 2 INCHES WITH STRONGER
STORMS. SMALL HAIL IS POSSIBLE WITH STRONGER STORMS TODAY ALONG
WITH WIND GUSTS OF 40 TO 50 MPH...BUT THE MAIN THREAT WILL BE THE
HEAVY RAINFALL AND INTENSE LIGHTNING.

ADDED MENTION OF HEAVY RAIN WEST TO INCLUDE BILLINGS AND ROUNDUP.
INCREASED PRECIPITATION CHANCES THIS MORNING WITH AN EARLY START
TO CONVECTION. NO CHANGE TO GOING FLASH FLOOD WATCH AS IT IS
LOCATED IN THE MOST FAVORABLE POSITION FOR STRONG SLOW MOVING
STORMS...HOWEVER AS WE HAVE SEEN ALREADY IN BIG HORN COUNTY WE
CAN`T RULE OUT LOCALIZED FLASH FLOODING FURTHER WEST INCLUDING THE
BILLINGS AREA TODAY. CHAMBERS

&&

.SHORT TERM...VALID FOR TDY AND WED...

THE PATTERN HAS TURNED FROM HOT AND DRY TO COOLER AND MORE
UNSETTLED. THE HOT UPPER RIDGE OF THE LAST SEVERAL DAYS HAS BEEN
PUSHED EAST BY AN ADVANCING UPPER TROUGH MOVING IN FROM THE WEST.
THIS TROUGH WILL PUSH ACROSS WESTERN ZONES THIS MORNING...CENTRAL
ZONES EARLY THIS AFTERNOON...AND THE EAST THIS AFTERNOON AND
EVENING. THE STRONGEST ENERGY WILL SLIDE ACROSS WYOMING...BUT THE
NORTHERN EXTENT OF THE TROUGH STRETCHED TO SOUTHERN CANADA...SO
THERE WILL BE ADEQUATE FORCING AND MOISTURE FOR CONVECTION. AS FAR
AS MOISTURE IS CONCERNED...PWATS WERE ADVERTISED AT 1.5 INCHES
OVER THE EAST. THIS IS 3 STANDARD DEVIATIONS ABOVE NORMAL.
PERSISTENT SOUTHEAST WINDS HAVE BROUGHT DEWPOINTS UP INTO THE 50S
OVER THE EAST. STORMS WILL FORM THIS MORNING OVER WESTERN
ZONES...SPREAD IN CENTRAL ZONES LATE MORNING INTO EARLY
AFTERNOON...THEN FORM OVER THE EAST THIS AFTERNOON AND EVENING.
SHEAR WILL BE WEAK...LESS THAN 30KTS...SO SEVERE NOT A HUGE
CONCERN...OTHER THAN MICROBURST WINDS WITH COLLAPSING CELLS. WEAK
SHEAR AND STEERING WINDS WILL LEAD TO SLOW MOVING PULSING CELLS
THAT WILL HAVE HIGH INTENSITY RAINFALL RATES OVER THE EAST. THE
VERY HEAVY RAIN STORMS MAY EVEN BE AS FAR WEST AS BIG HORN AND
EASTERN YELLOWSTONE COUNTY WITH PWATS AROUND AN INCH. HRRR HAS
CELLS GOING UP OVER NORTHERN SHERIDAN COUNTY AND SOUTHERN BIG HORN
COUNTY AROUND NOON AND THEN DEVELOPS UNORGANIZED CONVECTION
FARTHER EAST THIS AFTERNOON. WILL LEAVE FLASH FLOOD WATCH IN
EFFECT.

HIGH TEMPERATURES WILL BE COOLER OVER WESTERN AND CENTRAL ZONES
WITH EARLIER CONVECTION DEVELOPMENT. THE EAST WILL HAVE ENOUGH
CLOUD BREAKS TO WARM BACK UP TO THE UPPER 80S. THE STORMS ARE
PROJECTED TO EXIT THE EAST OVERNIGHT. WEDNESDAY COULD POTENTIALLY
BE ANOTHER ACTIVE DAY AS A SHORTWAVE OFF THE CALIFORNIA COAST GETS
DRIVEN ACROSS THE NORTHERN ROCKIES. THIS SYSTEM WILL HAVE ACCESS
TO A TROPICAL LINK AS EVIDENCED BY WATER VAPOR...SO THERE WILL BE
JUICE FOR CONVECTION. THE DEEPEST MOISTURE LOOKS TO SLIDE TO THE
SOUTH. SHEAR WILL BE STRONGER...AROUND 40KTS...AND CAPES RISE TO
AROUND 800J/KG. CERTAINLY LOOKS LIKE ANOTHER GOOD CHANCE OF
THUNDERSTORMS...WITH A SEVERE STORM OR TWO A DEFINITE POSSIBILITY.
STORMS WILL BE HEAVY RAINERS...WITH THE TROPICAL CONNECTION AND
PWATS ADVERTISED AT AROUND AN INCH. TWH

.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...

A FEW CHANGES WERE MADE TO THE EXTENDED FORECAST PERIOD THIS
MORNING...MAINLY CENTERED AROUND TIMING OF THE WEDNESDAY SYSTEM
EXITING THE REGION ON THURSDAY.

FOLLOWING THE EXIT OF THE SYSTEM ON THURSDAY...THE RETURN OF
UPPER LEVEL RIDGING WILL KEEP THE PATTERN DRY THROUGH SATURDAY
EVENING...WHEN THE NEXT PACIFIC TROF PUSHES INTO THE REGION. THIS
IS PROGGED TO BE ANOTHER WET SYSTEM...BRINGING PACIFIC
MOISTURE...AND TAPPING INTO MONSOONAL FLOW AS WELL. THE WAVE
HOWEVER DOES NOT SEEM TO BE HOLDING TOGETHER VERY WELL...GENERALLY
LOSING ORGANIZATION AND ENERGY AS IT APPROACHES. THEREFORE HAVE
KEPT POPS FAIRLY LOW...EVEN THOUGH IT HAS BEEN QUITE CONSISTENT
FROM RUN TO RUN. THIS WAVE...IF IT CONTINUES TO HOLD TOGETHER...WILL
CROSS THE REGION THROUGH SUNDAY...BRINGING SHOWER AND THUNDERSTORM
POTENTIAL ACROSS THE REGION ONCE AGAIN. TIMING ALSO SHOULD LEAD TO
COOLER TEMPS FOR SUNDAY...BUT STILL IN LOW 80S AT THIS POINT.

AT THIS POINT MODELS DIVERGE A BIT...BUT DO AGREE ON SOME DEGREE
OF SOUTHWEST FLOW INTO THE WESTERN MOUNTAINS...AND UPPER LEVEL
RIDGING BRINGING TEMPS APPROACHING 90 DEGREES ACROSS THE REGION
AGAIN. AAG

&&

.AVIATION...

NUMEROUS SHOWERS AND THUNDERSTORMS EXPECTED ACROSS THE AREA TODAY.
EMBEDDED STORMS WILL MAKE DIFFICULT FLIGHT CONDITIONS AT TIMES
INTO THIS EVENING. VERY HEAVY RAINFALL WILL CREATE MVFR TO LOCAL
IFR CONDITIONS NEAR SHOWERS AND STORMS. A COLD FRONT WILL PUSH
THIS ACTIVITY EAST THIS EVENING WITH VFR CONDITIONS PREVAILING
ACROSS THE AREA OVERNIGHT. CHAMBERS
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY WED     THU     FRI     SAT     SUN     MON
-------------------------------------------------------
BIL 079 059/084 058/085 056/083 057/085 058/083 059/089
    6/T 34/T    52/T    11/U    13/T    32/T    21/B
LVM 077 053/080 050/081 049/083 051/081 052/080 052/086
    6/T 35/T    52/T    11/B    13/T    44/T    32/T
HDN 084 056/087 057/087 054/085 055/088 057/085 057/091
    7/T 43/T    52/T    11/B    12/T    22/T    21/U
MLS 089 059/088 061/086 058/084 057/086 060/083 059/090
    7/T 82/T    54/T    11/B    13/T    33/T    31/B
4BQ 088 058/088 059/085 057/083 057/085 059/084 058/089
    7/T 72/T    52/T    21/U    12/T    33/T    31/B
BHK 088 058/086 059/082 056/081 054/083 057/080 056/085
    4/T 82/T    44/T    22/W    12/T    44/T    32/T
SHR 079 052/086 054/083 052/083 054/085 055/082 054/088
    6/T 43/T    52/T    11/U    13/T    32/T    21/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING FOR ZONES
      31>33-36-37-58.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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